The proposed project has been designed to provide an in vitro model for the study of hepatic fibrinogen synthesis. The model system which has been developed is an adaptation of a chick embryo liver cell culture technique, which supports the growth of hepatic parenchymal cells. The assay which is used to quantitate the fibrinogen in the cells and media is electroimmunodiffusion, using specific anti-fibrinogen antiserum. The model system will be used to study the effects of steroid hormones, both natural and synthetic, on fibrinogen metabolism. The mechanism of the effects of these hormones will be investigated using inhibitors of RNA and protein synthesis. A study will also be made of the order of synthesis and assembly of the fibrinogen molecule. The system proposed offers the opportunity to study the effects of hormones and drugs including those used for oral contraception on an isolated, controlled, and defined model of fibrinogen synthesis. It can be used to test newly developed hormonal agents for their effects and thus may serve as a preliminary screening system for the effects of new drugs of this component of the coagulation system.